7
Alexander Grothendieck et al. Séminaires en Géometrie Algèbrique- 4, Tome 1, Exposé 1
(or the Appendix to Exposée 1, by ‘N. Bourbaki’ for more detail and a large number of results.
AG4 is http://modular.fas.harvard.edu/sga/sga/pdf/index.htmlfreely available in French;
also available here is an extensive
http://planetmath.org/?op=getobj&from=books&id=158Abstract in English.